1. Field of the Invention
The invention relates to electrical switching apparatus, such as, for example, circuit interrupters and, more particularly, to circuit interrupters employing a slot motor. The invention further relates to slot motors. The invention also relates to slot motor housings.
2. Background Information
Circuit interrupters, such as circuit breakers, are employed in diverse capacities in power distribution systems. A circuit breaker may include, for example, a line conductor, a load conductor, a fixed contact and a movable contact, with the movable contact being movable into and out of electrically conductive engagement with the fixed contact. This switches the circuit breaker between an on or closed position and an off or open position, or between the on or closed position and a tripped or tripped off position. The fixed contact is electrically conductively engaged with one of the line and load conductors, and the movable contact is electrically conductively engaged with the other of the line and load conductors. The circuit breaker may also include an operating mechanism having a movable contact arm upon which the movable contact is disposed.
In order to enhance the speed of separation of the separable contacts, the contacts may be disposed within a slot motor, which increases interruption performance. Ring-shaped or loop-shaped slot motors typically have two assemblies, an upper assembly and a lower assembly. Both of the upper and lower assemblies include a corresponding insulative housing and a plurality of plates composed of magnetically permeable material (e.g., steel), which surrounds the separable contacts and the movable contact arm of the circuit breaker. The lower assembly is disposed below the fixed contact. When the power circuit is live, an electrical arc may be drawn between the separable contacts during separation. The electrical current interacts electromagnetically with the slot motor to induce a magnetic field in the magnetic material of the slot motor, which, in turns, interacts with the separating contacts and the movable contact arm to accelerate the contact opening process. Examples of slot motors are disclosed in U.S. Pat. Nos. 4,375,021; 4,546,336; 4,546,337; 4,549,153; 4,970,482; 5,694,098, and 6,281,459.
As shown in FIG. 1, the upper assembly is an inverted U-shaped assembly having a housing assembly 1 and a plurality of steel lamination plates 2, forming a bight portion 3 and two legs 4,5. The upper slot motor assembly is structured to be disposed over the movable contact (not shown) wherein the tips of the upper assembly legs 4,5 contact the lower slot motor assembly (not shown). The upper assembly legs 4,5 have an extended length to accommodate the path of travel of the movable contact arm (not shown). That is, the movable contact (not shown) is disposed between the upper assembly legs 4,5 and as the movable contact moves between the first, open position and the second, closed position, the movable contact moves from a position adjacent to the upper assembly bight portion 3 to a position adjacent the tips of the legs 4,5. Accordingly, the legs 4,5 have a sufficient length to accommodate the path of travel of the movable contact arm.
The one-piece housing assembly 1 is molded from a suitable plastic that may cause warping of this molded component. For example, a relatively large one-piece housing may come out of the mold (not shown) with the legs 4,5 being bent inward or outward, thereby making it difficult to insert the steel lamination plates 2 within the housing assembly 1 and, also, difficult to insert the inverted U-shaped assembly in the base of the circuit breaker (not shown).
Accordingly, there is room for improvement in electrical switching apparatus, such as circuit interrupters, employing a slot motor.
There is further room for improvement in slot motors.
There is also room for improvement in slot motor housings.